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<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>

  <style>
  
  </style>
</head>
<body>
  <div class="the_div">
    <p>我是p标签</p>
    <h3>我是h3</h3>
    <h3>我是h3</h3>
    <h3>我是h3</h3>
    <a id="theA" href="#">我是一个a标签</a>
    <ul>
        <li>北京</li>
        <li>天津</li>
        <li>南京</li>
    </ul>
    <ol class="my_li">
        <li>大张</li>
        <li>大王</li>
        <li>大狗</li>
    </ol>
    <ul class="my_li">
        <li>小明</li>
        <li>小红</li>
        <li>小蓝</li>
    </ul>
</div>
  <script>
    let id = document.querySelector('#theA')
    let h3 = document.querySelectorAll('h3')
    for(let i = 0 ; i<h3.length; i++){
      console.log(h3[i]);
    }
    let li = document.querySelectorAll('li')
    let li1 = document.querySelectorAll('.my_li li')
      li1.forEach(function(item){
        console.log(item);
      })
    const li2 = document.querySelector('ul.my_li li:nth-child(2)')
      li2.innerHTML = '小六'
      li2.style.color = 'red'
    let tian = document.querySelector('ul li:nth-child(2)')
    tian.classList.add('green')
    tian.style.backgroundColor = `lawngreen`
  </script>
  
</body>
</html>